The present invention relates generally to electrical stimulator leads. More specifically, the present invention relates to a method and apparatus for in situ testing of an integrity of electrical stimulator leads used in pacemakers.
Pacemakers include a housing containing electronic control and operational circuitry and either one or two electrical stimulator leads coupling the circuitry to a patient's heart. Two leads provide for a return path for electrical signals while a patient's body provides the return path when only one lead is used.
Installing a pacemaker in a patient requires a couple of surgical procedures. A first procedure implants the electrical stimulator leads directly into the heart. Ends of the leads opposite the electrodes inserted into the heart are brought near the surface of the skin, typically somewhere near the chest cavity. During a second installation operation, a surgeon implants the pacemaker housing near the skin surface of the patient and attaches the free ends of the stimulator leads. The reason for installing the pacemaker near the skin's surface is to permit servicing, or replacement, of the pacemaker on an outpatient basis. The stimulator leads, on the other hand, are permanently installed.
Pacemakers include many features to perform self-checking and testing of the circuitry to ensure proper operation. The electrical stimulator leads can fail as well, but they are not removed or serviced. Wires from the implanted electrodes are cut, leaving the electrode in the heart, and a new stimulator lead is implanted. The electrical stimulator leads typically consist of wires encased in a protective sheathing, insulating the wires. Due to the severity of the procedure to add new electrical stimulator leads, the leads are designed to last a long time. Unfortunately, in the prior art, there is no reliable way to monitor or judge when a lead is beginning to fail. Until the performance of the pacemaker system degrades significantly or fails, minor defects or failures that have developed over the life of the leads are undetectable.